Depends on the size of the service. 100 amp service will require 3 gauge, 150 amp service will require 1/0 gauge, and 200 amp service will require 3/0 gauge.
120 15 amp service ? 210 7 amp service ?
You should not load a 125 amp panel any more than 100 amps.
50 mm or 2 inch will handle the 3/0 wires for a 200 amp service.
For Service Entrance Cable 600 kcmill (Thousands of circular mils).
Depends on the size of the service. 100 amp service will require 3 gauge, 150 amp service will require 1/0 gauge, and 200 amp service will require 3/0 gauge.
Most apartments have a 60 amp panel for their electrical distribution.
Check the nameplate on the service panel. There it will tell you what the buss capacity is. On a 200 amp service nothing in the wiring configuration is allowed to be less than that the service rating. In the market there are 200 amp 42 circuit distribution panels.
7.75 amps
Yes, but at every reduction in wire size there has to be a breaker sized to the smaller wire size. The wire size for 100 amp panels is recommended at #3 copper conductor. From the 200 amp feeder panel you will require a 100 amp two pole breaker for each of the two 100 amp services. Keep in mind that if you run the 100 amp services close to maximum this will take away the capacity of the 200 amp service for other branch circuits coming off of it. Also keep in mind that if the panels are located, not in the same building as the 200 amp service that the 100 amp panels will be treated as separate services and will have to be constructed like a 100 amp service. This includes ground rods. Also the bonding screw will have to be removed that connects the neutral buss to the panel enclosure.
120 15 amp service ? 210 7 amp service ?
In the United States, there isn't a hard limit on how many 20 amp circuits that can be run on a 50 amp supply. This is because in most cases, especially in homes, we don't load most circuits with more than an amp or 2, even when they are protected by a 20 amp breaker. From a practical perspective you probably have a limited number of slots for breakers in your service or supply panel.
Normal home electrical service in most residential areas is provided at 120/240 volts. A 400 amp service would still typically be delivered at this voltage. The 400 amp rating indicates the maximum current capacity that the service can handle.
You should not load a 125 amp panel any more than 100 amps.
A 100 amp service provides less electrical capacity than a 200 amp service for a residential electrical system. This means that a 200 amp service can handle more electrical load and is better suited for larger homes or homes with higher electricity needs.
If the supply is a 20 amp supply it cannot supply a 40 amp stove, you need a bigger supply or a smaller stove.
50 mm or 2 inch will handle the 3/0 wires for a 200 amp service.